iPhone celebrates fifth birthday -- How has it changed?

Gadget fans may be focused on the CES trade show this week, but there's something else notable going on today: It's the iPhone's fifth birthday.
Five years ago today, Apple unveiled the original iPhone to the world. It wasn't a tightly kept secret, shrouded in mystery and speculation like more recent Apple announcements, but it was arguably the world's most anticipated gadget launch.
Although its form factor -- a capacitive touchscreen candy bar -- hasn't dramatically changed over the years, each iteration of the iPhone has yielded important improvements. Let's take a look back at how the iPhone revolutionized what we thought a phone could be.

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